1. Field of the Invention
This invention relates to an ink jet recording apparatus, and in particular to an ink jet recording apparatus wherein pressurized air generated by an air pressurizing pump is applied to a main tank serving as an ink cartridge storing ink, and a record head mounted on a carriage is replenished with ink from the main tank by the action of the pressurized air.
2. Description of the Related Art
An ink-jet recording apparatus produces comparatively low noise during printing operation and can form small dots at high density. Hence, the ink-jet recording apparatus has recently been used in a number of printing applications, including color printing.
Such an ink-jet recording apparatus is usually equipped with an ink-jet recording head which is mounted on a carriage and moved in the widthwise direction of recording paper, and paper feed means for moving the recording paper in the direction orthogonal to the traveling direction of the recording head. On the basis of print data, ink droplets are ejected from the recording head, thus recording the data on the recording paper.
The recording head is mounted on the carriage, and is capable of ejecting ink droplets of, for example, black, yellow, cyan, and magenta. Accordingly, the ink-jet recording apparatus enables full-color printing by changing the proportions of ink types, as well as effecting text printing with black ink.
Incidentally, in order to effect a comparatively-high volume of printing, a recording apparatus of this type supplied for, for example, an office or business purpose, requires use of high-volume ink cartridges. To this end, there has been provided a recording apparatus, in which main tanks serving as ink cartridges are fitted to a cartridge holder provided, for example, to an apparatus main body.
In the recording apparatus, sub-tanks are disposed on the carriage having the recording head, and the respective sub-tanks are replenished with ink from corresponding main tanks by way of ink supply tubes. The sub-tanks, in turn, supply ink to the recording head.
Recently, growing demand exists for a large-size recording apparatus capable of effecting printing on larger-size paper, in which a carriage travels a longer scan distance. In order to improve throughput of such a recording apparatus, a larger number of nozzles are provided in a recording head.
Further, demand exists for a recording apparatus which sequentially supplies ink to the respective sub-tanks mounted on the carriage from corresponding main tanks while performing printing operation, in order to improve throughput, and which stably supplies ink from the respective sub-tanks to the recording head.
In such a recording apparatus, since the ink supply tubes must be proved for connection between the main tanks and the sub-tanks on the carriage to correspond to the types of ink, and since the carriage travels over a longer scan distance, the lengths of respective ink supply tubes inevitably increase.
Further, as mentioned above, a larger number of nozzles are provided in the recording head. Hence, such a recording apparatus encounters a technical problem of deficient ink supply to the sub-tanks because the recording head consumes a large quantity of ink, and an increase in the dynamic pressure (i.e., pressure loss) of ink is likely to occur within each of the ink supply tubes interconnecting the ink cartridges and the sub-tanks.
As one measure to prevent this technical problem, there may be employed, for example, a construction in which air pressure is applied to the main tanks to forcibly inducing ink flows from the main tanks to the sub-tanks under air pressure.
An ink jet recording apparatus constructed as described above involves the following several problems to be solved:
First, in the construction for pressurizing the main tank, an air pressurizing pump is necessary for applying pressurized air to the main tank. A pressure regulating function capable of constantly applying stable air pressure to the main tank is required.
Second, an atmosphere release function is required for releasing the air pressure from the main tank during non-operated state in which power for the recording head is turned off, in order to eliminate, for example, a problem of inducing ink leakage from the main tank.
Third, in the construction for pressurizing the main tank, the air pressurizing pump should be driven all the time when power for the recording apparatus is turned on, in order to stably apply the pressurized air to the main tank and to assure proper operation of the ink supply system of this type.
However, in a case where the air pressurizing pump is driven all the time, there arise problems of noise produced by the air pressurizing pump, and durability of the air pressurizing pump. Therefore, another problem of cost increase associated with a countermeasure for these problems is also encountered.
Accordingly, a preferable approach required is to intermittently drive the pressurizing pump so that in the air pressure for each main tank is appropriately maintained within a tolerable range.
Fourth, a pressure detector is required for detecting air pressure given to each main tank. In this case, the following control can be adopted: If the air pressure detected by the pressure detector is equal to or less than a predetermined pressure value, the pressurizing pump is driven, and if the air pressure exceeds the predetermined pressure value, driving the pressurizing pump is stopped.
However, this control causes the following operation. That is, for example, as ink in the main tank is consumed even slightly based on the print operation, etc., the pressure detector detects a pressure value equal to or less than the predetermined value and the pressurizing pump is driven, and as the pressurizing pump is driven for a short period, the pressure detector detects a pressure value exceeding the predetermined value and the driving of the pressurizing pump is stopped.
This operation, in which the pressurizing pump is intermittently driven and stopped, is repeated thus repeated at extremely short time intervals. Therefore, a user may have a doubt that the recording apparatus malfunctions.
Fifth, a simple application of the above-mentioned construction causes another problem. Since pressurized air is applied to the ink cartridge forming the main tank detachably mounted to a cartridge holder, a careless removal of the ink cartridge from the cartridge holder causes ink to gush or splash out by the action of the pressurized air, thereby soiling the surrounding areas.
Since an outer shell member forming the ink cartridge receives the action of the pressurized air and is expanded in some degree, it is difficult to remove the ink cartridge from the cartridge holder. If the ink cartridge is removed forcibly, both the ink cartridge and the cartridge holder, particularly, an ink replenishment connection plug, etc., to which both the ink cartridge and the cartridge holder are connected, are deformed, causing damage to both the ink cartridge and the cartridge holder.
The sixth problem is as follows: Ink supplied from the main tank to the sub-tank in the ink jet recording apparatus of the above construction has a temperature depending property in which viscosity of ink is changed depending on environmental temperature; the viscosity is high at low temperature and is lowered as the temperature is increased.
Therefore, the velocity of ink replenishment flow from the main tank to the sub-tank has such a temperature depending property that the velocity is higher as the temperature is higher.
In the recording apparatus adopting the configuration wherein the sub-tank is replenished with ink from the main tank as described above, it is desired that the ink replenishment flow velocity from the main tank to the sub-tank should fall within a given range independently of the environmental temperature.
In this case, to suppress change in the ink replenishment flow velocity caused by change in the environmental temperature within a predetermined range, a control system is required to change the setup pressure of the pressurized air applied to the main tank in response to the temperature change.